You can simply return the key of the array (which is the family name):

foreach($families as $key => $family){
echo "FAMILY NAME = ".$key;
}

You can use the foreach just like ($array as $value) or like ($array as $key => $value). When the array is indexed (numerical key) the $key returns the position of the index (0, 1, 2...). When the array is associative (named keys), the $key returns the name of the index (in your example, Brooks, Hilberts, ...)